The present invention relates to a method for surface treatment of friction members like brake discs, drums, clutch parts and, more particularly, to treatment of PMMC based members and friction members provided thereby.
Conventional brake discs are presently made of ferrous alloys/cast iron having satisfactory performance and remaining operative even at substantially elevated temperatures up to and above 700xc2x0 C.
However, the present tendency in the automotive industry to reduce the total weight of vehicles challenges new lighter materials to also penetrate this particular segment of vehicle construction. Furthermore, improved corrosion resistance, as well as wear resistance, which increase the lifetime of the friction members up to the expected life period of the vehicles, are traits when looking for replacement of the present ferrous materials.
Consequently, several patent applications have been filed world-wide recently disclosing use of PMMC (Particle Metal Matrix Composite, such as an Al-alloy matrix reinforced by ceramic particles) based components used for different actual applications in vehicles. Shortcomings in common for all these applications based on PMMC base material are a softening phenomena at elevated temperatures, something which results in scoring and even plastic deformation of the members"" surface, thus considerably limiting the maximum allowed operating temperatures of the members. Therefore, as a remedy, it is instrumental to provide the basic PMMC-made friction members either with a special composite/-ceramic coating layer (thermal spraying of ceramics), or with a transfer surface layer.
The provision of an alternative transfer layer requires the layer to be both stable (adherent to the substrate and reliable) and homogeneous. Furthermore, fast formation of the layer having a sufficient thickness is also important both from a manufacturing, cost and performance point of view.
One feasible way to cope with the task of increasing the maximum operating temperature is simply to increase the volume percentage of reinforcing particles. Unfortunately, two major disadvantages connected with this xe2x80x9csolutionxe2x80x9d, namely increased costs of the PMMC base material and difficulties related to production/casting and especially cutting/-machining of the surface, eliminate this as a possibility for a cost efficient manufacturing method.
It is therefore an object of the present invention to provide a novel, fast and cost efficient method of manufacturing friction members that avoid the above mentioned drawbacks and difficulties connected to the conventional methods and products. Another object of the present invention is to provide a fast developing and homogeneous transfer layer exhibiting more stable friction properties, especially at high operating temperatures. Still another object of the present invention is to provide better protection for the base matrix material against scoring. Still another object of the present invention is to provide better protection for the base matrix material against scoring. These and other objects and features of the present invention are met by a method of manufacturing friction members as discussed below.